abstract

In a paper presented at OMA 2001, an extension of the panel code WAMIT was described where the surface geometry of the structure is represented explicitly and the solution for the velocity potential is approximated by higher-order B-splines. This permits an exact representation of the geometry in many applications, and avoids the effort and approximations inherent in preparing traditional low-order panel inputs. However the algorithms for the explicit geometry definition must be coded in special ad hoc subroutines for each type of structure. In the present paper we describe recent work to integrate the programs MultiSurf and WAMIT, in a manner which circumvents the need for special subroutines. In most practical cases this leads to a substantial reduction of the work required to perform computations of wave effects on structures. MultiSurf is a CAD program which enables users to define surface geometry with a high degree of accuracy, efficiency, and generality. It has been used extensively to develop low-order panel input files for ships and offshore structures, as well as for a variety of other marine design applications. The fundamental approach is to represent each part of the surface which is smooth and continuous by a parametric surface ‘patch’, using appropriate surface constructions which allow these patches to be joined robustly. The kernel of MultiSurf, known as RGKernel, includes the necessary code to evaluate surface locations and derivatives. A close integration of MultiSurf and WAMIT has been achieved by linking RGKernel with WAMIT, so that the same geometry can be reproduced during the hydrodynamic analysis. This integration makes it possible for users to define the geometry of structures interactively in MultiSurf, and to transfer this representation to WAMIT without significant extra effort. Thus the hydrodynamic analysis can be performed with exact or highly accurate representations of the geometry, and with the increased accuracy and efficiency inherent in the higher-order solution based on B-spline representation of the potential. After a brief explanation of the methodology, illustrative results are described for several examples. Comparisons are made of the accuracy, efficiency and workload, relative to the conventional use of low-order panels.

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